Redhead, It's 5 lands and grooves with a slanted side on the land walls. The R is for Russian, the originators of the design. ( I read that somewhere ) There are lots of bbl makers doing their own version of this style.
Rock Creek-- 5R = Russian
Satern ------- 5S = slanted
Broughton -- 5C = canted
Shilen -------- Ratchet , and many others. I was told a few days ago that Kreiger was doing one now also but I don't know that to be true.
They work well and claim to give higher velocity with less jacket deformation because of the slanted lands and the fact that there are no lands directly opposing each other in the bore.
Lots of guys here on LRH are using these bbls with good results, I'm sure they will tell you why!!
RHB